Hydraulic fracturing device and process

ABSTRACT

The present invention relates especially to a hydraulic fracturing device which comprises:—a tubular conduit ( 1 );—and, against its external face, a cylindrical sleeve ( 2 ) whereof the opposite ends ( 20 ) are connected together and hermetically to this external face;—the wall of said tubular conduit ( 1 ) comprising at least one opening ( 10 ) to have it communicate with the interior of the sleeve ( 2 ). This device is remarkable in that said sleeve ( 2 ) comprises at least one mechanical weakening zone ( 21 ) which is peripheral, sinuous and with closed contour, that is, its opposite ends rejoin, this mechanical weakening zone being capable of breaking under the effect of predetermined pressure ( 10 ) known as “burst pressure” applied to the interior of the latter to form in its wall a sinuous opening ( 3 ).

The present invention relates to a device for hydraulic fracturing of the rock of a well.

It also relates to a hydraulic fracturing process.

In the field of hydraulic fracturing it is common to make use of a casing placed inside the well to be fractured, a casing which is connected to sliding sleeves well known in the field of petroleum extraction.

These sliding sleeves are being used more and more in the field of hydraulic fracturing. They put the interior and the exterior of the casing in communication by means of holes or openings once they occupy a position which does not cover them.

These sliding sleeves can be activated by different systems the leading three of which are described herein below.

In the first place, use can be made of balls which are thrown from the surface of the well and which come to stop against the sleeves, causing them to move.

A mechanical tool or a spring which pushes (or pulls) on the sleeve to make it open or close can also be used.

And finally, differential pressure can be used such that it acts as a piston which moves the sleeve and uncovers the holes/openings.

These former known means have a number of drawbacks.

In the first place, the opening surface in the casing is limited due to the fact of the limited course of the sleeve (around 10 cm).

In the second place, these sleeves are located inside the casing so that they have limited resistance to external pressure. Their thickness is substantial to resist external pressure, reducing the internal diameter of the casing.

Also, their flow rate, that is opening speed, is slow (non-explosive).

Finally, they comprise machined pieces (as they slide and must be tight). This sleeve device therefore cannot be positioned on or in the casing. It must be screwed to the casing via two connections, which creates a weak mechanical point in completion.

Additional prior art is illustrated by EP-2 482 554 and GB-2 240 798.

The aim of the present invention is to solve the weaknesses in these prior techniques, especially for hydraulic fracturing applications.

Therefore, according to a first aspect of the invention the latter concerns a hydraulic fracturing device which comprises:

-   -   a tubular conduit;     -   and, against its external face, a cylindrical sleeve whereof the         opposite ends are connected fixedly and hermetically to this         external face;     -   the wall of said tubular conduit comprising at least one opening         to have it communicate with the interior of the sleeve,

characterised in that said sleeve comprises at least one mechanical weakening zone which is peripheral, sinuous and with a closed contour, that is, its opposite ends rejoin, this mechanical weakening zone being capable of breaking under the effect of predetermined pressure known as “burst pressure” applied inside the latter to form in its wall a sinuous opening.

Because the sleeve is positioned outside the conduit, it rests on the latter in the “non-ruptured” state and can therefore support considerable pressure. Also, it breaks “explosively” and opens up a wide opening allowing fracturing to be carried out in the best conditions.

According to advantageous and non-limiting forms of this device, taken singly or according to any combination:

-   -   said mechanical weakening zone comprises a region of reduced         wall thickness;     -   said weakening zone comprises at least one groove formed in the         external wall of said sleeve;     -   said winding comprises first portions of lines which extend         generally parallel to the generatrices of the sleeve which         alternate with second portions generally perpendicular to the         first portions, the extent of the first portions being greater         than that of the second portions.

Another aspect of the invention concerns a hydraulic fracturing process of the rock of a well which is characterised in that it comprises the following steps:

-   -   placing in the well a device such as described hereinabove;     -   making an annular seal between said conduit and the wall of said         well on either side of said metallic sleeve; and     -   injection inside said sleeve, via said conduit, of fracturing         fluid under fracturing pressure such that it is capable of         breaking the wall of the sleeve before the latter comes into         contact with the wall of the well.

Other characteristics and advantages of the present invention will emerge from the following detailed description of preferred embodiments. This description will be given in reference to the attached diagrams, in which:

FIG. 1 is a view in longitudinal section of a fraction of tubular conduit forming an integral part of the hydraulic fracturing device according to the invention;

FIG. 2 is a view similar to the preceding view after application inside the conduit of breaking pressure;

FIGS. 3 and 4 are perspective views of an exemplary embodiment of the sleeve of the fracturing device, corresponding respectively to the states of FIGS. 1 and 2; and

FIGS. 5 and 6 are similar views to FIGS. 1 and 2, the hydraulic fracturing device being placed inside a well.

The device according to the invention is illustrated in FIGS. 1, 2, 5 and 6, but appears partially only for ease of viewing.

In reference to both FIGS. 1 and 2, these illustrate only a fraction of a metallic tubular conduit 1 which is traditionally placed inside a well and, more particularly, in the horizontal part of the latter.

In practice, this conduit also comprises a vertical upstream end which terminates in the surface of the well, as well as a curved intermediate portion for joining the vertical part to the horizontal part.

It is a tubular conduit formed from several sections placed end to end so as to form a completion.

As is known per se, this tubular conduit comprises at least one opening 10 which has its internal space communicate with the exterior.

As will be become clear later in the description, it is via this type of openings that a high-pressure fluid is conveyed with the aim of fracturing the rock.

The attached figures illustrate only two circular diametrically opposite openings 10. However, it is possible to use a larger number of openings, for example four or six, distributed uniformly over the periphery of the casing. Openings with different shapes can also be employed.

Extending against the external face of this conduit is a cylindrical or approximately cylindrical sleeve 2 whereof the opposite ends 20 are connected solidly and hermetically to the external face of the conduit 1.

This is preferably a metal sleeve.

The sleeve is connected to the conduit 1 at the level of its ends 20 by means known per se, such as direct welding onto the conduit, or a machined assembly of a single piece with excess thickness at the ends. It is also feasible that the sleeve is connected by welding at the ends, in turn attached to the conduit.

The ends, respectively the thickness and/or attached ends, can optionally be crimped onto the conduit.

According to the invention, the sleeve 2 comprises at least one mechanical weakening zone which is capable of breaking under the effect of predetermined pressure, known as breaking pressure applied inside the latter to form a sinuous opening in its wall.

This zone is peripheral, sinuous and with a closed contour such that its opposite ends rejoin.

The situation in which the sleeve is broken is shown schematically in FIG. 2.

However, it might be preferred to refer to FIGS. 3 and 4 in which a possible embodiment of the sleeve 2 is illustrated.

In this case, this sleeve comprises a mechanical weakening zone comprising a region of reduced thickness, which here comprises a groove 21 formed in its external wall.

This groove is produced for example by machining, erosion, or by laser etching.

As already said this weakening zone has a closed contour such that its opposite ends rejoin.

In the embodiment illustrated here, optimal sinuous winding path is used, specifically said groove has an overall form similar to a set of hair pins arranged head to tail and connected together.

More precisely, this path comprises first portions of lines 210 which extend generally parallel to the generatrices of the sleeve and which alternate with second portions 211 generally perpendicular to the first portions, the extent of the first portions 210 being greater than that of the second portions 211.

In this case, the first portions 210 are between two and three times longer than the portions 211 and can extend over approximately 1 metre.

Of course, other embodiments are possible.

FIGS. 5 and 6 illustrate an exemplary embodiment of the hydraulic fracturing process according to the invention.

The first step in this process consists of placing in the well a device such as described hereinabove in reference to FIG. 1.

This is placed conventionally, that is, known per se, since a tubular conduit is used, which is simply modified on its external part.

An annular seal is then made between the conduit 2 and the wall of the well A, on either side of the metallic sleeve 2.

The means which enable this sealing are referenced 4 in FIGS. 5 and 6. They are any sealing means of known type, such as deformable annular sleeves.

In a final step in the process according to the invention, fracturing fluid under fracturing pressure is injected inside the sleeve via the conduit 1, which is such that it is capable of breaking the wall of the sleeve 2, according to the path of the abovementioned weakening zone, before the latter comes into contact with the wall of the well A.

Of course, it will have been ensured earlier to close the downstream end of the conduit 1 so that circulation of the fluid occurs via the openings 10 only.

In this way, an opening of the sleeve of explosive type is used, that is, a quasi-instantaneous opening.

This result is obtained preferably by using sleeve material which has reduced elongation rate. Of course, this characteristic combined due to the fact that a mechanical weakening zone has been provided makes this opening easier.

The fact of having provided winding, such as that described in reference to FIG. 3, produces an opening 3 with alternating sections 30 and 31 which overall give a consequent opening surface for the fracturing fluid which passes through the opening and strikes the rock.

As mentioned above, the sleeve is opened instantaneously once the fracturing pressure is attained.

However, in the completely deformed state, the wall panels of the sleeve which border the opening 3 and which in the present case have a form of alternate T petals stop against the wall of the well.

By way of example, the breaking pressure of the sleeve is of the order of 200 bars.

Due to the device and process according to the invention a sleeve is therefore used which can be qualified as an explosive sleeve the advantage of which is to present a wide opening 3 over a length which can reach more than a metre.

Because this sleeve 2 is located outside the conduit 1, it can support substantial external pressure since it rests on the casing when in the non-open state.

Because it is slid on the conduit and is fixed there quite tightly, there is no weak zone in the conduit.

Since opening of the sleeve occurs by exerting internal pressure which then bursts it suddenly, this very fast, almost explosive, opening tends to produce fracturing in the rock of the well A.

Finally, placing at least one mechanical weak zone or weakening zone at the level of the surface of the sleeve creates a controlled explosion shape of said sleeve.

Of course, embodiments other than that of FIGS. 3 and 4 are possible.

However, the advantage of this embodiment described here is that it deforms with a wide opening without any material detaching from the body of the sleeve. In fact, the petals T obtained after opening stay connected to the body of the sleeve 2 without rejection of debris which might disturb fluid flow in light of fracturing. 

1. A hydraulic fracturing device which comprises: a tubular conduit; and, against its external face, a cylindrical sleeve whereof the opposite ends are connected fixedly and hermetically to this external face; the wall of said tubular conduit comprising at least one opening to have it communicate with the interior of the sleeve, wherein said sleeve comprises at least one mechanical weakening zone which is peripheral, sinuous and with a closed contour, that is, its opposite ends rejoin, this mechanical weakening zone being capable of breaking under the effect of predetermined pressure known as “burst pressure” applied inside the latter to form in its wall a sinuous opening.
 2. The device as claimed in claim 1, wherein said mechanical weakening zone comprises a region of the wall of reduced thickness.
 3. The device as claimed in any one of claims 1 or 2, wherein said weakening zone comprises at least one groove formed in the external wall of said sleeve.
 4. The device as claimed in claim 1, wherein said winding comprises first portions of lines which extend generally parallel to the generatrices of the sleeve which alternate with second portions generally perpendicular to the first portions, the extent of the first portions being greater than that of the second portions.
 5. A process for hydraulic fracturing of the rock of a well, wherein it comprises the following steps: placing in said well a device as claimed in any one of the preceding claims; creating an annular seal between said conduit and the wall of said well, on either side of said metallic sleeve; injection inside said sleeve, via said conduit, of fracturing fluid under fracturing pressure such that it is capable of breaking the wall of the sleeve before the latter comes into contact with the wall of the well. 